In electrostatography, for example xerography, electrophotographic imaging or electrostatographic imaging, an imaging process may include forming a visible toner image on a support surface such as a paper sheet, plastics, films, etc. The visible toner image is often produced by forming a latent electrostatic image on a charged photoreceptor, which can be transferred to an intermediate transfer belt, and then fixed onto the support surface using a heated fuser belt or a heated roll fuser to form a permanent image.
Toners for imaging devices such as electrostatographic printers may include at least a binder resin, a colorant, and one or more external surface additives that may be added in small amounts. Examples of external surface additives include, for example, silica, titanium dioxide, zinc stearate and the like. The properties of a toner are influenced by the materials and amounts of the materials of the toner. The charging characteristics of a toner also can depend on the carrier used in a developer composition, such as the carrier coating.
Alumina (Al2O3) is an example of a toner additive. A typical alumina particle has a crystalline structure and is generally of a similar size in all dimensions, with a rough exterior having, for example, sharp edges. An alumina particle is more charge neutral than either silica and titania. Alumina used as a toner additive has a mean diameter of between about 10 nanometer (nm) and about 200 nm. In certain instances, alumina may be used as a toner additive to lower negative charge or increase positive charge. Like most oxides, alumina may serve several purposes as an additive. For example, alumina may improve charge control, flow aid, and transfer aid, which in turn improves transfer of the toner from the photoreceptor to the intermediate transfer belt or from the intermediate transfer belt to the support surface.
Due to its small size, alumina may embed or impact into the surface of the toner under low throughput or high toner age conditions, and may therefore lose its effectiveness and result in a decrease in the development of the toner and the transfer efficiency of the toner from the photoreceptor to the support substrate to be printed. To overcome this problem, larger sized “spacer” additives may be used shield small size additives such as silica, titania and alumina from impacting into the toner surface. While using larger sized additives may improve the effectiveness of the smaller additives, they increase production costs and attach poorly to the toner surface. Further, the larger sized additives can contaminate various materials and structures, such as the developer material, developer housing, charging devices, photoreceptor, transfer devices, and fuser components.
Thus, there is a need for new surface additives that can provide high charge and reduced additive impaction with improved adhesion of the additive to the toner surface.